Motor mechanism



Oct. 25, 1960 w. sTELzr-:R 2,957,311

MOTOR MECHANISM Filed Deo. 28, 1956 ATTORNEY United States Patent MQTORMECHANISM William Stelzer, Bloomfield Hills, Mich., assignor toKelsey-Hayes Company, a corporation of Delaware Filed Dec. 2S, 1956,Ser. No. 631,106

Claims. (Cl. 60-52) This invention relates to a motor mechanism, andmore particularly to such a mechanism of the type employing ahydraulically operated booster motor particularly for operating vehiclebraking systems.

An important object of the invention is to provide a novel mechanism ofthe character referred to having a hydraulic booster and a mastercylinder arranged as a unit in axial alinement, thus greatly simplifyingthe construction.

A further object is lto provide such a mechanism wherein the hydraulicmotor is adapted to be operated by uid displaced by a motor employed foroperating a power steering mechanism, and wherein a follow-up action ofthe motor piston is secured through the operation of a1 throttlingvalve, controlled directly by the brake peda A further object is toprovide an apparatus of the character referred to wherein the piston ofthe hydraulic motor lhas a portion directly engageable with the plungerof the master cylinder to transmit direct forces from the pedal to themaster cylinder piston, and wherein the throttling valve which controlsenergization of the hydraulic motor, and the parts associated therewith,are so arranged in normal positions as to provide for the freecirculation of hydraulic fluid through the motor without effecting anyactuation thereof.

A further object is to provide an apparatus of this character wherein aprogressively increasing hydraulic reaction against the brake pedal isprovided, whereby a normally soft initial pedal is provided as isdesirable, and wherein hydraulic reactions against the pedalprogressively increase throughout the range of brake application.

A further object is to provide novel motor control means whereby threestages of pedal operation are provided, namely, a soft initial stageoperating solely against light spring pressure; a second or intermediatestage in which limited and progressively increasing hydraulic reactionsare transmitted to the brake pedal as the motor is energized, and athird stage in which progressively heavier hydraulic reactions aretransmitted to the brake pedal.

Other objects and advantages of the invention will become apparentduring the course of the following description.

In the drawing I have shown one embodiment of the invention. In thisshowing:

The gure is an axial sectional view through the motor and mastercylinder, parts being broken away and parts being shown in section, theother elements of the brake system being diagrammatically represented.

Referring to the drawing, the numeral 10 designates a preferablydie-cast body one end 11 of which constitutes a master cylinder in whichis arranged a plunger 12' having heads 13 and 14 arranged at oppositeends thereof, the head 14 being sealed in the master cylinder as at 15.The head 13 is provided with a lipped cup 16 and is movable to the leftof the normal position "ice shown in the drawing to generate pressure ina master cylinder chamber 17.

The master cylinder is provided with a conventional residual pressurevalve 20 and a return spring 21 is interposed between this valve and thelipped cup 16 to bias the` plunger 12 to the normal position shown.Fluid from the chamber 17 passes through the residual pressure valve 2i)in the usual manner and ows through suitable hydraulic lines 22 to thevehicle wheel cylinders 23.

'I'he master cylinder is provided thereabove with a chamber 26communicating with the space behind the head 13 through the usual port27. Just ahead of and immediately adjacent the lip of the cup 16 a smallreplenishing port 27' communicates between the chamber 26 and thechamber 17. The chamber 26 is supplied with hydraulic lluid through aline 28 connected to any suitable type of reservoir 29.

The right-hand end of the body 10 constitutes a hydraulic motor,comprising a cylinder 34 the internal diameter of which is appreciablylarger than the internal diameter of the master cylinder 11. Thecylinder 34 is provided therein with a piston or plunger 35 dividing thecylinder 34 to form inlet and outlet chambers 36 and 37 respectively.

The piston 35 is sealed in the cylinder 34 as at 38, and to the left ofthe seal 38 is arranged a floating bearing 39 arranged in a slot 40surrounding the piston 35 and maintained in position longitudinally ofthe piston 35 by a ring 41.

The chamber 36 communicates through a passage 44 with a bore 45 withinthe plunger 35. The piston 35 rearwardly of the bore 45 has an enlargedbore 46 in which is arranged a disk valve 47 normally engaging theshoulder between the bores 45 and 46 and provided with an axial opening48.

On the rear end of the plunger 35 is threaded a cap 50 carrying anintegral rearwardly extending tubular piston 51 in which is slidable arod 52. The piston 51 slides in a bearing 53 threaded in the rear end ofthe motor cylinder 34, and the piston and bearing are sealed withrespect to each other as at 54. It will be noted that the rear end ofthe forward portion of the cap 5.0 seats against the inner end of thebearing 53 to limit rearward movement of the plunger 35.

A cap 58 is threaded on the rear end of the piston 51 and forms abearing in which is slidable a collar 59 carried by the rod 52 the rearend of which is connected as at 61 to a conventional brake pedal 62.

The inner or left-hand end of the rod 52 is reduced as at 60 and isreceived in the recessed rear end of a head or valve 64 normally spacedfrom the valve 47 to provide for normal communication between the bores45 and 46. The latter bore communicates through a passage 65 with apassage 66, formed in the piston 35 forwardly of the groove 4%. Theforward end of the passage 66 communicates with the motor chamber 37. Itwill become apparent that with the parts in the normal positions shown,uid can flow freely between the chambers 36 and 37.

Rearward movement of the head 64 is limited by a washer 68 serving tomaintain in position a seal 68' surrounding the stem 6G. The head 64 isbiased for rearward movement by a relatively light spring 69. Thisspring is surrounded by a second heavier spring 70 which biases thevalve 47 against its seat as shown in the drawlng.

An axial rod has its rear end threaded in the plunger 35 and is providedin such rear end with a bore 76 adapted under conditions to be describedto communicate with the bore 45. This communication is normally cut offby a ball valve 77 biased to closed position by cally'illustrated andindicated .by the numeral 88.

3 a spring 78. The bore 76 communicates with the chamber 37 throughports 79.

Between the chambers 17 -and 37, the body 10 is provided with a tbore85) in which :is arranged arbearing through which the rod 75 projectsinto :engagement with the ,plunger `head 14. The bearing 81-is sealed.as 'at "82 relative to the rod 75, and the space between gthe fhead 114and bearing 81 is vented -to Ythe :atmosphere as at .83.

A 'hydraulic pump associated with the power :steering mechanism (notshown) of the vehicle is diagramm'tli'- i e outlet of this pumpcommunicates through -a hydraulic line 89 with a port 90 leading intothe chamber Fluid -is supplied to the .pump :88 .through a line 91leading from the zusualrsump'92. r

The chamber .37 is provided with :an outlet .95 connected gto `oneend-.of afhydraulic line 96 leading -to the conventional steering valve$97 :and from this valve a return yline98 leads `to the -fsump 92. Arelief valve indicated Yas a 4whole by vthe numeral 99 is interposedbetween and connected to the pipes L96 and 98 respectively by lines.S100 ,and 101. The relief valve is provided with anfinternalchamber 102:in which is 'arranged a'ball valve 1.03 normally Vseated by a'spring104 'to cut v.olf communicationxhetween the lines 100 and 101, it :beingunderstood'that .the -valve 103 will open when -a predetermined pressureis present :in 7the line 96.

Operatz'on valve, the iluid being by-p'assed 'in the conventional`manner :through the relief valve99 v5to the sump :92. .'l'he .rod 75and tubular piston 51 are .of the same diameter, hence the eifective endfaces of the piston .35 .subject to pressures in Ithe chambers 36 and 37are equal. Thus .there will beV no K4differential Vpressures tending tozmove the piston '35, and this piston will be maintained "in fits normalposition by -the spring V21 in Vthe master Icylinder chamber T17,l Y Y`flo operate the mechanism, the operator will depress the jbrake pedal62. Ihe collar 59 will slide inzthe Shearing 58 and ythe rod52'will-move tothe Ileft so thatits lefthand end approaches the valveVport '.48 vto :restrict the flow of iluid -between the chambers '36 and37. This initial movement o'f fthe rod 52 takes place solely against thecompression of lthe light spring 69 thus providing a V softinitialpedal.

eter than the valve port 48 and accordingly is adaptedY to close such:port At the time of the initial building up :of Vdifferentialfpressures in Vthe manner Vdescribed to move the piston 35 toward theleft, 4pressures in the chamber 36 will act Vagainst `the left-hand .end`of the head 64, thus Aproviding hydraulic reaction against .the

' 4 vto .the .left of .the valve 47 by -restricting .ow of .uid throughthe port 48, higher. pressures will exist in the chamber 36 than in thechamber 37 and movement of the piston will continue; If movement of therod 52 is arrested, a very slight additional movement of the piston 35will crack the port 48 to communication with the bore 46, thuspreventing .an additional building up of pressure in the chamber A36`:and .arresting movement of the piston 35.

Assuming that lbrake operation :is continued, additional pressure on thebrake :pedal will-cause -the v-left vend of the head 64 to remain in.engagement with .the disk valve 47 to maintain the va'lve port 48closed.v YThus pressure in the chamber 36 will be built uptthrough athird stage of brake operation, and when the pressure in the chamber 36reaches a predetermined point, it will react against the valve disk 47to crack this valve from its seat. Reaction :now :be applied in tthe rod:and to the brake lpedal proportionate Jo `the total area lof fthevalve#disk 47.V Thus -in :the .third stage of valve Aoperation -aproportionately heavier hydraulic yreaction fis applied to ythebrakezpedal.

l ,Assuming athatlthe hydraulic :motor lis energized to the maximum-extent permitted 'by means described below, and .aifurther-"hrakeapplication .is desired, -aheavier pedal pressure, acting through therod 52, disk Valve @7 'and plunger. 35will vassist the pressure .1in thechamber 36 in generating .higher 4pressures -in `'the master cylinderchamber :17.

Y r.lt is l.well known vthat operation Vrif the steering valve of ahydraulic vpower .steering mechanism, such vas the valve 9.7.,icausesithe generation of back pressure between Y the steering valve andthe pump. 'Ihis is true, of course,

in the present case, 'and accordingly, upon )operation of the steeringwaive, :pressure will 'develop in the lines :89 and 96-and alsoin thermotorfclambers. 'and237. 'This does not in any wayzatlect -the .booster:motor `of the pres- I en't invention when ithe flatteriis :notoperating, since preslbrake pedal inthe second stage of brake operation.It

will be obvious that the left end of the head 64 in cooperation withAthe valve disk 47 acts as a .throttling means controlling the ow of uidbetween the chambers36 and 37 and consequently controlling'thepressurein the chamber 36 during the stage of operation referred 'to, thethrottling valve means acting in the nature of a followup valve'device.`So 'long as the rod '52 follows movement sures will stillfhe balancedin ithe motor I'chambers 36 and 3,7 :and he esame piston :areas will be`exposed :to -these chambers :for ihereason that the fsleeve 51 `and rod,575 are of the tsame :cross :sectional area.

A different situation exists, however, if the brake being :operated :andfthe .steering wheel is `thenturned, but the 'characteristics .of thepresent .construction iare such that the actual functioning-of fthebrake applying mechanism -will :not be atected. `Assuming .that rthebrke vhas been 'operated :and the :steering wheel is kthen "turned, backpresslutewilloccur'iin the motor chamber -37 `and will l'tend morelightly .to .seat the valve '.64, .or the .disk A47], if lthe second:stage of brake voperation is taking place. vIn lsuch case the backpressure will tend to assist the .operator-in thrott-ling the :ow ofiluid from he .chamber .36 to 'the chamber 37, `thus `causing an.immediate incr-ease Vin pressure in :the chamber 36'due tothe'actioniof the pump l88. fincrease in ypressurerin dhe .chamber 36,takes lplace nntila point reached nt which `.the motor #throttlingvalve device will function strictly in accordance withforcebeinglapplie'd to :the brake :pedalrby'the operator. "It'is aninherentfcharacteristc ofthe boostermotor of thezpresent case,therefore, in an open system of the kind described, for the valvefmechanism immediately to adjust .itself to any variation in hydraulicuidconditions in the system due .tooperation .of .the steering valve. Inother words, WhetherV the vbrake pedal .is .operated while the steeringmechanism Yis inoperative, .or,the steering mechanism becomes operativeafter initiation of afbrake application, the braking operation is 'stillperfectly `under the control of the operator .both as to the function.of applying the brakes 'and as'to theapplication of reaction to vthebrake pedal.

It isjnecessary, ofcourse, tomaintainthe ow of hydraulic "Huid 'foriuseVby the steering valve and, in view of the capacity of the kpump 88, itIis v'further -necessaryto limit the vgeneration of pressures in `thechamber 36.

For this purpose, the ball valve 77 is provided. In practice, the spring78 is so loaded as to maintain the valve 77 closed up to pressures ofpreferably about 400 p.s.i. in the chamber 36. This pressure representsthe maximum energizing pressure which can be built up in the chamber 36,and beyond such pressure the valve 77 will open for the flow of uid frombore 45 into the bore 76, thence through ports 79 into the chamber 37and through hydraulic line 96 to the steering valve 97 and relief valve99. Thus adequate pressure will be providedfor operating the steeringvalve while the brakes are applied, and excessive pressure in thechamber 36 is prevented.

It will be apparent that in the event of a failure of hydraulic pressurefor operating the motor, the brakes are still subject to manualoperation. Depression of the brake pedal will move the inner end of therod 52 into engagement with the disk 47, thus manually moving theplunger 35 and transmitting movement directly through the axialextension 75 to the master cylinder plunger 12. Thus fluid will bedisplaced from the master cylinder chamber 17 directly by pedalpressure.

It will be apparent that the hydraulic motor is arranged in thehydraulic steering circuit between the pump 88 and the steering valve97. The ow of hydraulic uid to the steering valve thus is through thehydraulic motor. 1f, while applying the brakes, the steering wheelshould be turned to operate the steering valve 97, a back pressure willoccur through line 96 in the chamber 37, providing some tendency to buckagainst the piston 35, and thus transmit an undesirable increasedreaction against the rod 52 and hence against the pedal 62. The device,however, is so constructed as to minimize such increased reactioneffect. Upon the occurrence of the back pressure in the chamber 37, suchpressure will be transmitted through passages 66 and 65 to the bore 46to act against the portion of the right-hand side of the disk 47outwardly of the head 64, thus subjecting the disk 47 to a pressuretending to maintain it in closed position, this force being in additionto the force exerted by the operator. Moreover, under the conditionsdescribed the valve or head 64 will be in engagement with the disk 47,and the righthand end of the Valve 64 will be subjected to the sameincreased pressure tending to assist the operator in maintaining thehead 64 against the disk 47. The reduction in the size of the stem 60increases the area of the head 64 subjected to such pressure. The backpressure referred to thus will be utilized to assist the operator intransmitting force to both of the elements 47 and 64, and theundesirable increase in reaction against the pedal 62 will be minimized.

The present mechanism provides a coaxial arrangement of all of the partsof the motor, the valve mechanism and its operating means and the mastercylinder, thus facilitating the manufacture and assembly of the partsand providing for an economical manufacture of the apparatus. The use ofthe oating bearing 39 is desirable in eliminating problems ofconcentricity involving the hydraulic motor piston. lt will be notedthat the piston 35 has clearance with the wall of the cylinder 34, thuspermitting the plunger to be freely movable in the bearings 53 and 81without any binding action of the piston 35 in the cylinder 34. The seal38 effectively seals the chambers 36 and 37 from each other and thefloating bearing 39, while iixed against movement longitudinally of thepiston 35, may alter its position radially of the piston to accommodatefor any linaccuracies in the concentricity of the motor cylinder and thebearings 53 and 81.

Attention is invited to the fact that when the parts are in the normaloperating positions shown, the circulation of hydraulic uid through themotor maintains pressure in both chambers 36 and 37. The axial extension75 and sleeve 51 preferably are of equal diameter so that the piston hasnet equal areas subject to pressures in such chambers. In the offpositions of the parts, therefore, there are no diierential pressurespresent in the chambers 36 and 37, the pressures therein always beingapproximately equal, and accordingly there is no tendency for the motorpiston 35 to creep toward the left. If desired, the axial extension 75may be made of slightly smaller diameter than the sleeve 51, thusproviding the piston 35 with a net area exposed to the chamber 37slightly greater than its area exposed to the chamber 36. In this casewhen pressures are balanced in the chambers 36 andV 37 there will be anet effective pressure tending ,to maintain the piston 35 in its normaloit position. In any event, therefore, the diameter of the sleeve 51should be at least as great as the diameter of the axial extension 75.

Thev throttling valve per se for controlling the followup action of thehydraulic motor piston is disclosed and claimed in my copendingapplication Serial No. 625,070, filed November 29, 1956, now Patent No.2,913,877, granted November 24, 1959.

It is to be understood that the form of the invention shown and'described is to be taken as a preferred example of the same and thatvarious changes in the shape, size, and arrangement of the parts may bemade as do not depart from the spirit of the invention or the scope ofthe appended claims.

I claim:

l. A motor mechanism comprising a casing and a piston therein dividingsaid casing to form an inlet chamber and an outlet chamber, meanscarried by said piston comprising a normally open valve establishingcommunication between said chambers, constantly operating means forpumping fluid into said inlet chamber and discharging it from saidoutlet chamber, a disk forming a seat for said valve and having a normalposition in which it has an area substantially larger than the area ofsaid valve subject to pressure in said inlet chamber, and a springengaging said disk to bias it to said normal position, said disk havingan axial opening toward which said valve is movable against the ow offluid' from said inlet chamber to said outlet chamber to throttlecommunication between said chambers and to build up pressure in saidinlet chamber to effect movement of said piston, said valve when inclosed position having an area subject to pressure in said inletchamber, acting through said axial opening, to hydraulically reactagainst said valve, said spring being loaded to be overcome at arelatively high pressure against said disk whereby said area of saiddisk increases the hydraulic reaction against said valve, andwork-performing, motion-.transmitting means connected to said piston.

2. A motor mechanism comprising a chamber having a piston therein anddividing said casing to form an inlet chamber and an outlet chamber,bypass means normally connecting said chambers through said piston andcomprising a valve seat and a manually operable valve normally spacedfrom said seat, means constantly delivering hydraulic fluid to saidinlet chamber and discharging uid from said outlet chamber, said valvehaving one end engageable with said seat to throttle the ow of iluidthrough said valve seat from said inlet chamber to said outlet chamberwhereby pressure in said inlet chamber increases to effect movement ofsaid piston, an axial work-performing stem connected to said piston, amanually movable operating rod connected to said valve, said end of saidvalve being subject to pressures in said inlet chamber to hydraulicallyreact against said rod, said valve seat comprising a disk having anopening therethrough, said bypass means having a second valve seat ofsubstantially greater area than said opening and against which said disknormally seats, and a spring normally holding said disk on said secondseat against pressure in said inlet chamber whereby, upon a building upof pressure in said inlet chamber above a predetermined point, the areaof said disk within said second seat becomes etfective for transmittinghydraulic reactions to said rod.

3. A motor mechanism comprising a chamber having a.

piston therein and dividing said casing -to form an "inletYelramberrjand `an 'outlet chamber, bypassjmeans lnormally connectingsaid 'chambers 4through said `piston "and-coniprising avaveseat and amanually operable valvenorrna1l5l :spaced from saidseat, meansconstantly'deliveijing hydraulic uid to said inlet `chamber anddischarging iltiid from said outlet "chamber, said valve V:having Aoneend Lengageable with ysaid seat rto 'throttle the flow o lltiid "throughsaid y'valve "seat from said inlet chaniberito said `outlet chamberwhereby p ressurein said linlet*6:11am- `Aber'increases to electmovement "o'ffsaid piston, 'an 'axial work-performing stem-connected tosaidpiston,a manually movable operating rod connected to saidvalve,.'said end Yof said -valve `being' subject :to pressures :in:saidinlet fchamber to hydraulically react 'against vsaid frod, saidvalve seat comprising 'a 'disk having 'an opening vthereithroughfsaid'bypass means having a second valve seat 'of substantially greater areathan v,said opening and against :which said -disk normally seats, aspring 'normally holding saiddisk on'said second Yseat against pressurein said inlet chamber lwhereby, upon'a buildingupofpressure in-'saidf-inlet chamber above va predetermined point, the area of said diskwithin said second -seatbecomes Yeffective for transmitting hydraulicreactions to said 5rod, vand means connected between said chambers forbypassing 'duid rom said inlet Vchamber to -said outlet 'chamberwhen-the 'pressure Ein said inlet chamber increases to a predeterminedYpoint above the pressure 'at which said 'spring yields. l

4. A motor mechanism comprising 'a chamber having aal-piston therein'and dividing said casing to form an 'inlet chamber and an outletchamber, 'bypassmeans normally connecting 'said chambers through -saidpiston and' comprising a valve Vseat and a 'manually operable'va'lvevnormally spaced from `said seat, means constantly-delivering hydraulicduid to said inlet chamber `and 'discharging 'fuid from 'said outlet-'chamber, said 'valve 'having :one 'end-engageable with said se'attothrottle theow'of Huid through said valve seat 'from 'said Ainletchamber to said outlet 'chamber whereby pressure V'in said Vinletchamber increases to etiectmovemjent lof 'said piston, Van 'axialwork-'performing stem connected fto `said piston, va manually movableoperating rodconnected to said valve, said fendof said'valvebeingsubject to pressures in said inlet or chamber to :hydraulically reactagainst said rod, 'said valve seat comprising fa disk having an openingthere- 1throu'g`h, said 'bypass means zhaving afsecond valve seat of#substantially greater area than said opening and' against which saiddisk normally seats, a spring normally holding saiddisk on'said secondseat 'against'pressure lin'said inlet fcharnber whereby, upon abuilding'up-of pressure in said inlet chamber above a predeterminedpoint, .the 'area of said disk vwithin -said second seat becomes`effective for transmitting .hydraulic reactions to said rod, ysaidpiston having a bypass passage yconnected between said cham- 'bers andincluding a check valve, and a spring stronger than said "first 'springnormally 'holding said check valve closed against pressures in '-said-inlet chamber.

'5. A motor mechanism comprising a casing having a cylinder therein, apiston in said cylinder, an axially projecting stern carried by saidpiston, a bearing at one end vof said casing through which said stemextends, a `seal carried fby -said bearing vand surrounding said stem,said piston dividing said cylinder to 'form an inlet chamber K and anyoutlet chamber-and having peripheral clearance `A-with respect-to saidcylinder, -a lipped 'seal `carried by ksaid piston and engaging saidcylinder, 'a iloat'ing 'ring carried by said :piston and slidablyiitting said cylinder,

saidiring fbeing mounted for radial movement relative 'to Y l:saidpiston fand being fiixed against axial movement'rel'ative' to saidpiston and maintaining said last-named Yseal Ain position, normallyfopen 'bypass 'means 'connecting l'said `in'le't fand-outle't-ehambersand including-'a normally open throttlingvalve saidvalvebeing'moun'tedfor axial slidv ng movement coaxially of 'said piston'and having bear- 75 to form 'a pair of chambers, a bypass'communicating being means ffor supporting fit for suc'h '-movement, andmeans constantly supplying hydraulic l-lluid #to said inlet chamber and:discharging such Y"-,il'u'id ffrom jsaid outlet chamber, said valvebeingmcvdble towardclosed posi- :tion 'to lhro'ttle vflow Yof fluidthrough s'aidfbyp'ass 'means said'inle't chamberto said-outlet chamberwhereby :the `supplying 'o ihydraulic duid Yto 4said finlet chamberwill-'raisetheepressnre -therein andmove said piston. k ff lm'eghanism'according to claim 5 wherein -said bypass ,means Ai1'1' :lt:u:les avalveseatahaving lan `opening therethrough toward )which said throttlingEvalve is movable, said 4valve, when moved toward said seat, having anareaopentopressurein said inlet/chamber tofbe sub; jeetedtbhydranlicreactioninsuch chamber. y e

"7. A lmechanism according 'to 4claim 5 wherein said bypass meansincludes avalve 'seat having an opening therethrough ltoward which said:throttling valve is movable-said valve, when moved toward *said seat,fhav'ing 'an area lopen to `pressure Yin 'said 'inlet 'chamber -to "bestilijected to Ihydraulic reaction in such chamber, means connectedbetween *said inlet `and Y'outlet chambers and 'stbject xto 'an increasein pressure in 'said linlet Ychamber to fapredetermned point'forbypassing duid from `said in'let 'chamber to 'said 'outlet 'cham'ber,and Ameans ysub'- ject "to :pressure in said 'inlet chamber landoperative bellow vsaid predetermined "pressure therein forproportionately increasing the 'hydraulic reaction against saidvalve.

48. Afmechanism according toclaim 5 wherein said bypass means `includes"avalve seat having 'an Vopening `therethrough toward vwhich 'saidthrottling vvalve is movable, said valve, ,when moved toward 'said seat,having an area 'open to pressure in 'said inlet 4chamber to be subjected'to lhydraulic 'reaction in `such chamber, means 'connected jbetweensaid inlet and outlet chambers and subject 'to an increase Ain pressurein `said 4inlet chamber to 'a 'predetermined 'point for bypassing 'iluidfrom said Ainlet chamber `to said `'outlet chamber, 'said `valve 'seatcomprising 'a Adisk having said opening therethrough 'towardwhi'c'h:said valve is movalileito throttle `communieation through said bypassmeans, `said Adisk having ta seat `aaginst 'which it i's engageable and'having an 'area greater 'than 'the varea of said valve exposed topressure in said inlet `chamber, Tand 'a spring normally holding `saiddisk ,against 'its seat, said :spring 'being .adapted to 'yield at apredetermined pressure whereby Apressure in said inlet chamber,'actinga'gain'st said disk,'will Lbeltransmitted to said valve ftoproportionately increase the hydraulic reaction thereagainst. o Y

9. A motor mechanism comprising a casing having 'a coaxially movablepiston therein, a bearing at 'one 'end o't 'said casing, a'work-'performing iaxial extension carried vby said ,piston andVprojecting through said bearing,

vsaidgpiston dividing said casing to 'form .an inlet chamber `fromtsaidoutlet chamber, the end of -said' valve movable toward said valve Aseatbeing exposed to pressure in 'said inlet chamber to provide hydraulicreaction Aagainst said rod when said valve is moved towardsaid-seatrsaid seat comprising a ydisk of substantially greater areathan said valve, a 'second 'seat `carried `by .said piston ,and 'against'which 'said disk seats, and a spring biasing said disk against 'saidsecond se'a't 'against pressure in said inlet ehanib'er.

T0. A motor mechanism comprising a rcylinder having spaced lheads and apiston therein dividing said' cylinder tween said chambers, means forcontinuously supplying hydraulic iluid to one of said chambers, meansfor discharging hydraulic uid from the other of said chambers, a rstvalve seat in said bypass, a -throttling valve arranged in said bypassand opening away from said seat toward said other chamber, biasing meansnormally maintaining said valve in open position, said bypass beingprovided with a rst chamber and a second chamber, the former of whichcommunicates with said one motor chamber and the other of whichcommunicates with said other motor chamber, a second valve seat betweensaid irst and second chambers opening toward said second chamber, sairrst valve seat forming a valve engageable with said second seat, springmeans biasing said rst valve seat toward said second valve seat, andmeans connected to said valve to transmit force thereto move it towardsaid valve seat to throttle the flow of uid therethrough and thus buildup pressure in said one chamber, said piston having stems of equaldiameter slidable in said heads whereby said piston has equal areasexposed to uid in said chambers.

References Cited in the le of this patent UNITED STATES PATENTS VickersDec. 6, Staude Aug. 8, Guernsey May 29, Hofstetter Sept. 20, MastellerMay l2, Chouings May l1, Baldwin Aug. 10, Carr et al. Nov. 16, ParnellMar. 7, Banker June 16, Edge Dec. 8, Edge Jan. 5, Sprague et al. June 8,Kane Aug. 9, Fitch et al. May 22, Ayers July 29,

